Phase behavior and ionic conductivity of lithium perchlorate-doped polystyrene-b-poly(2-vinylpyridine) copolymer

The phase transitions of lithium perchlorate (LiClO₄)- doped polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) were studied as a function of temperature and ion salt concentration using in situ small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Incorporation of LiClO₄ into an asymmetric, disordered PS-b-P2VP copolymer produced temperature-dependent order-disorder (ODT) and order-order transitions (OOTs) from spherical to lamellar microphases. The effective interaction parameter (π_eff) between two block components was evaluated for low molecular weight LiClO₄-doped PS-b-P2VP in a disordered state. With increasing quantities of LiClO₄, a remarkable increase in π along with a volumetric change produced by the selective coordination of LiClO ₄ to the ionophilic P2VP block led to morphological transitions from disordered (DIS) to body-centered cubic spherical (BCC) to hexagonally packed cylindrical (HEX) to lamellar (LAM) structures. We also demonstrate that the ionic conductivity in the samples quenched from the different structures is morphology-independent, while it increases with increasing salt concentration.